A plasma processing apparatus for performing predetermined plasma processing on a semiconductor wafer or a substrate such as a flat display panel commonly includes an accommodating chamber (hereinafter, referred to as a “chamber”) that accommodates a substrate. In such a substrate processing apparatus, high-frequency power is applied to the chamber while the processing gas flows into the chamber, such that plasma is generated from the processing gas, thereby performing the plasma processing on the substrate by the generated plasma.
When the high-frequency power is applied to the chamber, there are some cases where abnormality such as plasma abnormal discharge (for example, micro-arching) occurs due to various factors. The plasma abnormal discharge generates a crack or a notch on the substrate surface, or damages constituent components disposed in the chamber by a fire, and also generates particles by releasing deposits attached to the constituent components (for example, upper electrode) in the chamber.
For that reason, it is necessary to detect the plasma abnormal discharge in early stage, such that, when the plasma abnormal discharge is detected, appropriate countermeasures, for example, to stop an operation of the plasma processing apparatus are rapidly performed, thereby preventing the damage to the substrate or constituent components and the generation of the particles. Accordingly, various methods for detecting the abnormality such as the plasma abnormal discharge or the like in early stage have been developed.
For example, as a method capable of performing high-sensitive detection of the plasma processing method, a method for detecting an acoustic emission (AE) caused by energy discharge in the plasma abnormal discharge has been considered. As a detection apparatus using the AE, detection apparatuses is known, in which a plurality of ultrasonic sensors are disposed on an outer wall of a chamber, and the ultrasonic sensors detect the AE caused by energy discharge when the plasma abnormal discharge occurs, or in which a plurality of acoustic probes are installed so as to be in contact with a loading plate (susceptor) that loads a semiconductor wafer, or a focus ring disposed around the semiconductor wafer loaded on the loading plate, and an ultrasonic wave propagating the acoustic probes is detected by the ultrasonic sensor (for example, see Patent Document 1). In this case, a method for monitoring high-frequency power (voltage or current) used for generation of the plasma may be used in combination.